The finding by United States researchers is based on analysis of data from the Dunedin Study.
It has worldwide health implications, the scientists said in an article published in the Journal of the American Medical Association today.
Many countries still experienced high lead exposure through contaminated water, soil, paint and pipes.
The Dunedin Study offered the largest and longest psychiatric follow-up to date of adults who had their lead levels tested when they were children.
It was also the only study to have have continually assessed psychopathology symptoms later in those people's lives and broadly measured personality disorders, lead author Aaron Reuben said.
''These results suggest that early-life lead exposure in the era of leaded gasoline experienced by individuals who are currently adults may have contributed to subtle, lifelong differences in emotion and behaviour that are detectable at least up to 38 years of age.''
Of the original 1037 people in the Dunedin study, just over half were tested for lead exposure when they were 11 - and 94% of them had blood lead levels above the current level where clinical attention is recommended.
People who had high childhood blood lead levels ended up testing higher on psychopathology tests than those with low lead levels.
The researchers said while lead might not be the main cause of adult psychiatric disease, their findings were similar to studies which had measured the effect of lead on IQ, and were stronger than those found in a study on lead levels and criminal offending.
''On a population basis, even modest alterations in risk can lead to significant shifts in the overall burden of disease,'' the article said.
''The finding that associations between childhood blood lead levels and psychopathology symptoms were observable ... suggests that lead-related alterations in emotion and behaviour, however modest, likely emerge early and persist across the life course.''
Dunedin Study director Richie Poulton said yesterday the US research had not found a strong effect from lead levels on mental health, but its findings merited further study.
''Examining the relation between childhood lead exposure and subsequent later life mild cognitive decline may continue to be a research theme,'' he said.
''There might be a very small risk to mental health in adulthood following high levels of exposure to lead during childhood - but at levels that no longer occur in New Zealand.
''Independent replication is required before more concrete conclusions can be drawn.''
Dr Poulton said when the Dunedin Study researchers tested blood lead levels 30 years ago, they were looking for evidence of short-term behavioural, cognitive and educational effects.
''Given recent interest on the lead issue consequent [to] the water crisis in the American community of Flint, we have generated a series of follow-up papers.''
